Process for forming high salt content complex greases



July 8, 1958 A. J. MORWAY ET AL 2,842,495

PROCESS FOR FORMING HIGH SALT CONTENT COMPLEX GREASES Filed Nov. 22, 1954 u so Arml Inventors Hons G. Vesterdal By wzflwmnmtomey United States Patent PROCESS FOR FORMING HIGH SALT CONTENT COMPLEX GREASES Arnold J. Morway, Clark, and Hans G. Vesterdal, Elizabeth, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application November 22, 1954,Serial No. 470,436

8 Claims. (Cl. 252-39) the invention relates to an improved method for preparing such greases and to the improved greases produced thereby. I

Soap-salt complexes are well known in the art for thickening lubricating oils to produce lubricating grease compositions. These complex thickeners have been employed for high temperature greases and consist of combinations of metal salts of low molecular weight carboxylic acids with metal soaps of high molecular weight fatty acids. Normally the soaps and salts have been employed in proportions in the range of about 0.5 to 3 moles of salt per mole of soap. Because the thickening effect of the salt is rather low, it has been generally considered desirable to maintain the mole ratio of salt to soap below 3 since above a mole ratio of about 3 the total requirement of soap-salt thickener needed to make greases of satisfactory penetration characteristics was found to be quite high.

However, recently it has been found that by drastically increasing the salt content and with it the metal content of soap-salt complexes, entirely new properties may be built into these complexes which greatly increase their value as grease thickeners. More specifically, it has been found that complexes of metal salts of low molecular weight carboxylic acids with metal soaps of high molecular weight carboxylic acids which contain at least 7 moles and up to as much as 40 moles or more, preferably about 8 to 25 moles, of the low molecular Weight acid per mole of the high molecular weight acid have outstanding loadcarrying, dispersant, and various other beneficial characteristics in addition to thickening properties comparable to soap-salt complexes containing substantially lower proportions of low molecular weight carboxylic acids. These particular thickeners and their utilization in lubrieating grease compositions are described in detail in the co-pending Morway and Kolfenbach application Serial No. 387,527, filed October 21, 1953, which is assigned to the same interest as the present application.

Heretofore these lubricating greases containing a soapsalt complex having a molar ratio of salt to soap in the range of about 7:1 to 40:1 were prepared by forming a grease-forming mixture of a lubricating oil, at least one salt-forming low molecular weight carboxylic acid, at least one soap-forming high molecular weight carboxylic acid, and a basic reacting compound of at least one grease-forming metal and heating the mixture to an elevated temperature in a grease-making zone to dehydrate the composition and to promote formation of the soapsalt complex. During this heating step, the bulk temperature of the grease was generally maintained in the range of about 450 to 600 F.

It has now been found that the lubrication life of these high salt content complex greases may be increased by subjecting at least a portion, generally at least about 10% 2,842,495 Patented July 8, 1958 by weight and preferably at least about 20% by weight, of the contents of the grease-making zone to a temperature in the range of about 700 to 1100" F. The resultant greases formed in accordance with this invention have a greater hardness for a given soap content than do the conventional high salt content complex greases. This greater hardness therefore means that an improved grease yield may be obtained since for a given hardness a lesser amount of the soap-forming ingredients need be utilized. This is economically advantageous since the soap-forming ingredients are relatively expensive. The subjection of at least a portion of the grease to the grease-hardening temperature in the range of about 700 to 1100 F. may be accomplished in a number of ways. For example, the grease-forming ingredients may be intimately mixed in a grease kettle having skin or surface temperatures in the range of about 700 to 1100 P. so that at least a portion of the contents of the grease kettle is subjected to the grease-hardening temperature while maintaining the bulk grease temperature in the range of about 450 to 600 F. Also for example the grease-forming ingredients may be heated in a grease kettle having surface temperatures not exceeding about 600 F. so that the bulk grease temperature is maintained in the range of about 450 to 600 F. and then at least a portion of the grease may be withdrawn from the grease kettle and passed through a heating unit where it may be heated to the grease-hardening temperature by indirect heating. More specifically after the conventional high salt content complex grease is formed in such a kettle, the entire contents may be passed through such a heating unit in order to obtain the desired result of this invention. As an alternative, during the grease-making procedure at least a portion of the contents of the grease kettle may be passed through the heating unit and recycled back to the greasekettle while maintaining the bulk grease temperature in the grease kettle in the range of about 450 to 600 F. The grease subjected to the grease-hardening temperature in the range of about 700 to 1100 F. is maintained at that temperature for a period of time suflicient to substantially decrease the worked ASTM penetration thereof after 60 strokes at 77 F., i. e. by at least about 10 mm./l0. The greases of this invention areprepared with conventional salt-forming low molecular weight carboxylic acids, conventional soap-forming high molecular weight carboxylic acids and conventional lubricating oils such as mineral oils and/or synthetic oils. Preferably the grease-forming metal is an alkaline earth metal such as calcium.

The high molecular weight carboxylic acids useful for the purposes of the present invention are the soap-forming acids and include those having about 12 to 30 carbon atoms and preferably those having about 16 to 22 carbon atoms per molecule. These acids may be derived from saturated or unsaturated naturally occurring or synthetic fatty materials. The fatty acids normally used in the manufacture of conventional greases, particularly the more saturated acids, are preferred. Examples of such acids include stearic, hydroxy stearic, such as l2-hydroxy stearic, di-hydroxy stearic, poly-hydroxy stearic and other saturated hydroxy fatty acids, arachidic, hydrogenated fish oil and tallow acids, etc. However, unsaturated acids, such as oleic, ricinoleic and similar acids may likewise be used. It will be understood, of course, that the naturally occurring or synthetic fatty materials men tioned above may be directly employed in the greasemaking process to form soaps of high molecular weight carboxylic acids by treatment thereof with the basic metal reacting compound in the grease-making process. Mixtures of these high molecular weight carboxylic acids may be employed if desired.

Suitable low molecular weight acids include saturated and unsaturated aliphatic monoand poly-caboxylic acids having about 1 to 6 carbon atoms such as formic, acetic, propionic, furoic, acrylic, adipic, and similar acids including their hydroxy derivatives such as lactic acid, etc. Formic and particularly acetic acids are preferred. Mixtures of these low molecular weight acids may be employed if desired.

The metal component of the complex thickeners 'of this invention may be any grease-forming metal but is preferably an alkaline earth metal such as calcium, strontium, barium and magnesium, the preferred alkaline earth metal being calcium. Mixtures of the grease-forming metals may be employed if desired.

The lubricating oil employed to produce lubricating grease compositions in the method of this invention may be mineral as well as synthetic lubricating oils. The synthetic oils include synthetic lubricating oils having a viscosity of at least 30 SSU at 100 F. such as esters of monobasic acids (e. g. ester of C Oxo alcohol with C Oxo acid, ester of C OX alcohol with octanoic acid, etc.), esters of dibasic acids (e. g. di-Z-ethyl hexyl sebacate, di-nonyl 'adipate, etc.), esters of glycols (e. g. C Oxo acid diester of tetraethylene glycol, etc.), complex esters (e. g. the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethyl-hexanoic acid, complex ester formed by reacting one mole of tetraethylene glycol with two moles of sebacic acid and two moles of 2-ethyl hexanol, complex ester formed by reacting together one mole of azelaic acid, one mole of tetraethylene glycol, one mole of C Oxo alcohol, and one mole of C Oxo acid), esters of phosphoric acid (e. g. the ester formed by contacting three moles of the mono methyl ether of ethylene glycol with one mole of phosphorus oxychloride, etc.), halocarbon oils (e. g. the polymer of chlorotrifluoroethylene containing twelve recurring units of chlorotrifluoroethylene), alkyl silicates (e. g. methyl polysiloxanes, ethyl polysiloxanes, methyl-phenyl polysiloxanes, ethylphenyl polysiloxanes, etc.), sulfite esters (e. g. ester formed by reacting one mole of sulfur oxychloride with two moles of the methyl ester of ethylene glycol, etc.), carbonates (e. g. the carbonate formed by reacting C Oxo alcohol with ethyl carbonate to form a half ester and reacting this half ester with tetraethylene glycol), mercaptals (e. g. the mercaptal formed by reacting 2-ethyl hexyl mercaptan with formaldehyde), formals (e. g. the formal formed by reacting C Oxo alcohol with formaldehyde), polyglycol type synthetic oils (e. g. the compounds formed by condensing, butyl alcohol with fourteen units of propylene oxide, etc.), or mixtures of any of the above in any proportions. Also, mixtures of synthetic and mineral lubricating oils in any proportions may be employed. Quite generally the mineral or synthetic oils should have a viscosity within the range of about 35 to 200 SSU at 210 F. and flash points of about 350 to 600 F. Lubrieating oils having a viscosity index of 100 or higher may be employed. However, oils of lower viscosity index such as below 60 V. I. give better yields. For certain applications, other lubricating oils such as vegetable and animal oils may be employed if desired either alone or in admixture with mineral and synthetic oils.

The lubricating oils utilized in the high temperature grease-making procedure of this invention are preferably mineral oils or non-saponifiable synthetic lubricating oils. However, if in the grease-making procedure the grease is dehydrated at a relatively low temperature, such as in the range of about 250 to 350 F., prior to heating the grease to a temperature of at least about 450 to promote formation of the soap-salt complex, saponifiable synthetic lubricating oils may be employed in the greasemaking procedure of this invention. However, in any event, saponifiable synthetic lubricating oils may be added to the grease after the grease-making procedure when the grease has been cooled below a temperature of about through conduit 13 from jacket 11. of kettle 10 is regulated by means of valves Maud 15 450 F. Also, other synthetic lubricating oils and mineral oils may likewise be blended with the grease compositions of this invention after the grease-making procedure is completed.

The complex soap-salt thickeners of this invention generally will represent about 5 to 35%, preferably about 10 to 25%, of the total lubricating grease composition. The molar ratio of the salt formed from the low molecular weight carboxylic acid to the soap of the high molecular weight carboxylic acid should be at least about 7:1 and preferably is in the range of about 8:1 to 25:1. Molar ratios as high as about 40:1 or higher may be employed if desired. In general, the lubricating oil will represent about 55 to by weight of the total lubricating grease composition. It will be understood that conventional grease additives such as anti-oxidants, e. g. phenyl alphanaphthylamine, corrosion inhibitors, tackiness agents, load-carrying compounds, viscosity index improvers, oiliness agents and the like, may be added prior, during or after the heating steps, as will be apparent to those skilled in the art.

The grease-making procedure employed to prepare the high salt content complex greases of this invention comprises forming a grease-forming mixture of a lubricating oil, at least one salt-forming low molecular weight carboxylic acid, at least one soap-forming high molecular weight carboxylic acid and a basic reacting compound of at least one grease-forming metal, heating the mixture in a grease-making zone at a bulk grease temperature in the range of about 450 to 600 F. for a period of time sufiicient to promote formation of said complex and subjecting at least a portion, generally at least about 10% by weight and preferably at least about 20% by weight, of the contents of the grease-making zone to a greaseh-ardening temperature in the range of about 700 to 1100 F. for a period of time sufficient to increase the hardness of the grease. The period of time that the grease is subjected to the grease-hardening temperature should be sufficient to decrease the ASTM worked penetration (as described in ASTMD217-52T) thereof after 60 strokes at 77 F. by at least about 10 mm./l0. The finished grease preferably has a worked penetration in the range from about mm./10 to about 325 mm./10. The worked penetration of the grease subjected to the grease-hardening temperature should be decreased by at least about 10 penetration units and may be decreased as many as 50 or more units. Generally a residence time of about 0.2 to 5 minutes will provide such decreases in Worked penetration. Preferably, the grease-hardening temperature employed is in the range of about 800 to 1000 F. It will be understood that the residence time at the greasehardening temperature will depend upon the greasehardening temperature employed as well as the degree of hardness desired.

The invention will be best understood by reference to the drawing which is a diagrammatic illustration, shown in partial cross section, of apparatus adapted to carry out a preferred embodiment of the method of this invention. Referring now to the drawing, reference numeral 10 designates a grease-making kettle which is equipped with a. heating jacket 11. A heating medium, such as steam, Dow-Therm, hot flue gases, or the like, may be introduced through conduit 12 into jacket 11 and removed therefrom The rate of heating in conduits 12 and 13, respectively. Kettle 10 is provided with motor 20 which operates shaft 21 to which are connected a number of paddles, such as paddles 22 and 23, which are adapted to thoroughly mix the contents of kettle 10.

The lubricating oil utilized in forming the grease cornpositions is stored in tank 30 and may be passed therefrom through conduit 31 into kettle 10 by operating valve 32 in conduit 3].. The low molecular weight carboxylic acids are stored in tank 33 and may be introduced into kettle through conduit 34 by operating valve 35 in conduit 34. The high molecular weight carboxylic acids are stored in tank 36 and may be introduced into kettle 10 by means of conduit 37 by operating valve. 38 in conduit 37. The basic reacting compound, such as an oxide, hydroxide or carbonate, of the grease-forming metal is stored in tank 40 and may be introduced into kettle 10 through conduit 41 by operating valve 42 arranged in conduit 41. It will be understood that additional storage tanks and conduits may be provided so that conventional additive materials such as anti-oxidants and the like may also be introduced into kettle 10 during the greasemaking procedure.

"The grease-making process of this embodiment of the present invention may be initiated by opening valve 32 in conduit 31 to permit lubricating oil stored in tank 30 to flow into kettle 10. Valve 43 in outlet conduit 44 of kettle 10 is in a closed position. Motor 20 is then started so as to'operate shaft 21 so that the contents of k'ettle 10 are thoroughly stirred and mixed by means of paddles22 and 23. Valve 35 in conduit 34 is then opened to permit the low molecular weight carboxylic acid, such as acetic acid, to flow from tank 33 into kettle 10. Then valve 38 in conduit 37 is opened to permit the high molecular weight carboxylic acid, such as hydrogenated castor oil and/ or hydrogenated fish oil acids, to flow from tank 36 through conduit 37 into kettle 10. Thereafter, valve 42 in-conduit 41 is opened in order to introduce the basic reacting compound of a grease-making metal, such as hydrated lime, into kettle 10; The proportions of ingredients are selected to form a grease-making mixture and so that the molar ratio of low molecular weight carboxylic acids to high molecular weight carboxylic acids is in the range of about 7:1 to 40:1 and preferably in the range of about 8:1 to 25:1. A suflicient quantity of the metal compound is introduced to substantially neutralize the low and high molecular weight carboxylic acids. A heating medium, such as Dow-Therm, diphenyl oxide, steam, hot oil or flue gas, or the like, is then introduced into jacket 11 of kettle 10 through conduit 12 and the spent or cooled heating medium is subsequently withdrawn'from jacket 11 through conduit 13. The rate of heating is controlled by means of valves 14 and in conduits 12 and 13, respectively. The temperature of the heating medium is adjusted such that the temperature of inner wall 16 of kettle 10 does not exceed about 600 F. As the temperature of the contents of kettle 10 is raised, they are dehydrated and the resultant water vapor is removed from kettle 10 by means of vent 17 in the upper portion of kettle 10. Heating is continued until the bulk temperature of the contents of kettle 10 is increased to a temperature in the range of about 450 to 600 F., preferably about 500 F. At this point, a conventional; high salt content complex grease has been formed.

Now, inaccordance with this invention, valves 43 and 46 in, outlet conduits 44 and 47, respectively, are opened and pump 45 is started in operation in order to pump the -56 in conduits 53 and 54, respectively. The gaseous products ofwcombustion from furnace 52 pass'upwardly out of furnace 52 through conduit'57 into the lower portion of heater 51. A dense fluidized bed 60 of finely divided solids, such as finely divided silica-alumina, having a particle size'substantially in the range of about 10 to 100 microns, is maintained within heater 51 extending from thelower portion thereof to an upper level indicated by the reference letter L. Furnace 52 and'heater 51 are designed such that the superficial velocity of the flue gases fronffurnace 52 passing upwardly through bed 60 is in the range of preferably about 0.5 to 1.5 feet per second.

After the flue gases have passed upwardly through fluid bed 60, they rise above level L into disperse phase 61 and pass through inlet 62 of cyclone separator 63, which may be any conventional cyclone separator adapted to separate finely divided solids from a gas. In cyclone separator 63 entrained finely divided solids are separated from the flue gas and are returned to dense bed 60 by means of dipleg 64, and theessentially solids-free flue gas is removed from cyclone separator 63 by means of conduit 65. The exit flue gas in conduit'65 may be passed through heat exchangers (not shown) to recover its sensible heat. The operation of such fluidized solids systems is well understood by those skilled in the art, particularly in the oil refining art, of such processes as fluid catalytic cracking, fluid hydroforming, and the like.

The utilization of dense fluid bed 60 provides efii'cient heat transfer from the heating medium in heater 51 to the grease flowing through heating coil 50 in heater 51. The temperature of heater 51 is adjusted such that the inner skin or surface temperature of heating coil 50 is at least about 700 F. Temperature as high as 1100 F. or higher may be employed. Preferably the skin temperature of the inner surface of heating coil 50 is maintained in a temperature range of about 800 to l,000 F. The temperature in heater 51 may be regulated by controlling the rate of introduction of fuel and air to furnace 52. An additional control of the temperature in heater 51 may be obtained by introducing stem into the lower portion of heater 51 through conduit 68 by regulating valve 69 in conduit 68. Y

The grease from kettle 10 is therefore passed through heating coil 50 in heater 51 wherein the grease is subjected to a grease-hardening temperature in the range of about 700 to 1100 F. The residence time of the grease in heating coil 50 is preferably at least sufi'icient to increase the hardness of the grease passing therethrough such that the worked penetration thereof after 60 strokes at 77 F. is decreased by at least 10 mm./l0. However, if desired, the worked penetration may be decreased -up to 50 penetration units or more; The residence time of the grease in heating coil 50 is regulated by controlling the speed of pump 45. Generally a residence time in the range of about 0.2 to 5 minutes will be sufiicient to provide a satisfactory grease in accordance with this invention having improved properties, particularly increased hardness and increased lubrication life. Longer residence time up to one hour may be allowed if the temperature does not exceed the thermal decomposition temperature of the lubricating oil.

After the grease has passed through heating coil 50, it flows through conduit 70 into cooler 71 which may be any conventional indirect cooler wherein the grease temperature is reduced below about 600 F. The cooled grease from cooler 71 is then passed into conduits Hand 74 by opening valve 73, through which conduits the grease maybe passed to homogenization and/or packaging units (not shown) or to storage.

As an alternative procedure to the embodiment described above, the following procedure may be employed. After the various grease-formingingredients have been introduced into kettle 10 and heating has begun by introducing the heating medium into jacket 11, as described previously, valves 43 and 46 may be opened to permit the contents 'of kettle 10 to be pumped by means of pump 45 into heating coil 50 operated under the conditions previously described. After flowing through heating ,coil, 50, the material is passed through conduit 70, through cooler 71 and thenthrough conduits 72 and 75, by opening valve 76 and closing valve 73, back into kettle 10. If desired, cooler 71 may be by-passed by means not shown or the cooling system ofcooler 71 may be shut down. If the cooling step is not employed, the residence time of the material in heating coil 50 should be reduced to compensate for the additional residence time .at the .grease+hardening temperature which occurs inconduits .72 and 75.

Thus :it will .be seen in this alternate procedure that a vportion of the contents of kettlell) is withdrawn therefrom, passed through heating coil 50 in heater 51 and recycled back to kettle during the grease-making procedure. This recycle operation through heating coil 50 is continued until the bulk temperature of the con tents of kettle 10 has reached a temperaturein the range of about 450 to 600 F. At this point, the grease is completed and a high salt content complex grease has been formed which has improved lubrication life and increased hardness. ,If desired, additional hardness :may

he obtained bypassing the finished grease through heating coil 50 while maintaining the bulk grease temperature below about 600 F.

The grease may then be cooled in kettle .10 by passing a cooling medium through jacket 11 through conduits 12 and 1.3 if desired. The finished grease is withdrawn through conduit 44 by opening valve 43 and is'pumped through conduit 80 byopening valve 81 in conduit 80 and closing valve 46 in conduit 47. The grease passing through conduit 80 may be passed to homogenization and/or packaging apparatus (not shown) or may be passed to storage.

The method of this invention may be also carried out in a one-step procedure by employing a specially designed heating kettle having inner surface temperatures (those surfaces in contact with the greasesforming ingredients in the kettle) of at least about 700 F. and up to about 1100 F. Thus grease kettles may be designed which have flames impinging directly on the outer kettle walls to provide an inner kettle wall temperature of at least about 700 F. Such kettles should be provided with highly eflicient mixing apparatus because it is necessary that the grease-forming ingredients remain at the high temperature periphery of the greasernaking zone for only a limited period of time and are thereafter withdrawn such that additional grease-forming materials may contact the high temperature kettle surface. In this particular procedure, it will be understood that while a peripheral portion of the greaseforrning materials in the grease-making zone (the grease kettle) is heated to a temperature in the range of about 700 to ll00 F., the bulk temperature of the total grease is not permitted to exceed about 600 F. Bulk temperature, as used in this specification, refers to the total heat content of the total grease, or total greaseforming materials, divided by the weight of the total grease, the quotient being expressed as temperature. Thus in this particular embodiment of the method of this invention, the grease-forming materials are heated in a grease-making zone wherein a peripheral portion of the contents of the grease-making zone is subjected to temperatures in the range of 700 to 1100 F. while the bulk .grease temperature is raised to a temperature in the range of about 450 to 600 F. o

Other methods of carrying out the method of this in- .vention will be apparent to those skilled in the art and it will be understood that such modifications are to be considered as a part of this invention.

The invention will be more fully understood by reference' to the following examples. It is pointed out, however, that the examples are given for the purpose of illustration onlyand are not to be construed as limiting the scope of .the present'invention in any way.

EXAMPLE 1 Preparation of high salt content complex greases by conventional method .Twodiiferent high salt content complex greases were prepare employing conventional greascmaking procedures. These eases,rwhichwillher inafterheztermed crease Aiand grease :13, had :iollowing formulations;

l-Iydrogcnnted fish oil acids corresponding to commercial stoaric acid'in number of carbon atoms and in degree of saturation.

2 Oxidation inhibitor.

3 A naphthenic type mineral oil having a viscosity of SSU at 210 F- Each of .the above greases was prepared in the following manner. A mixture was prepared in a grease kettle consisting of the hydrogenated castor oil, the Hydrofol acids 51, the hydrated lime, and the lubricating oil. These'ingredients were heated in the grease kettle by circulatingfthrough the kettle jacket Dow-Therm having a maximum temperature of about 560 F. When the ingredient temperature was raised to F., the acetic acid was charged and the grease heated to about 500 F. bulk grease temperature. The temperature of the inner surface of the grease kettle did not exceed 560 F. throughout the grease-making procedure. It required about 5 hours to raise the contents of the kettle to 500 F. After the bulk grease temperature had reached .500 F. heating was discontinued and cooled Dow-Therm was circulated through the kettle jacket. When the grease had cooled to about 250 F the phenyl alpha naphthylamine was added. The grease was then cooled to below about.200 F.

Preparation 0] high salt content complex greases by method of this invention Two different high salt content complex greases were prepared in accordance with this invention. They will hereinafter he referred to as grease C and grease D, and they .had the following formulations:

1 Hydrogenated fish oil acids corresponding to commercial stcaric acid in number of carbon atoms and in degree of saturation.

2 Oxidation inhibitor.

4 ,A naphthenic type mineral oil having a viscosity of 55 SSU at 210 F.

It will-be noted that the formulations of grease C and grease D were identical with the formulations of grease 'A and grease B, respectively. Grease C and grease D were prepared by the following procedure. All of the ingredients were added to a grease kettle. Heating was initiated and the ingredient bulk temperature was raised to about 500 F. This heating step, which required about 2 hours, was accomplished by heating the kettle by direct-impingement of large gas flames directly on the bottom and side walls of the kettle so arranged as to cause hot-spots of high temperature in excess of 700 F. The inner surface temperature of the grease kettle was about 800? .F. However, the bulk ingredient temperature did not exceed about 500 F. due to thorough stirring of the kettle contents.

Comparison of properties of greases All of the greases prepared as described above, that is greases A to D, had an excellent appearance. However, .the greases -;prepar ed, in accordance with the method of this invention were substantially superior to the .grcases prepared by the conventional method with respect to both hardness and lubrication life. The hardnesses of the greases were as follows:

Penetrations 77 F. mm./

Grease Grease Grease Grease A B C D Unworked 219 206 195 24 1 Worked 60 Strokes 267 321 238 272 Worked 75,000 Strokes 323 375 308 350 The lubrication lives of these greases were as follows:

Grease: Lubrication life (hours) A (not tested). B 976 C 2402 D 2034 It will be noted that the penetrations of the greases prepared by the method of this invention ranged from 6 EXAMPLE 2 A large sample of grease A, which was described in detail in Example 1, was reheated in a grease kettle which was heated by direct impingement of gas flames directly on the bottom and side walls of the kettle. The inner kettle wall surface had a temperature of about 800 F. During the reheating step, the contents of the grease kettle were thoroughly stirred and heating was discontinued when the bulk grease temperature reached about 500 F. The heating step required about 3 hours. The resultant grease produced upon reheating grease A will hereinafter be referred to as grease E. Samples of grease A and grease F. were homogenized at 200 F. and other samples were homogenized at 100 F. The following hardnesses were determined for these grease samples:

Worked Penetration 1 After Homogenizatlon at 200 F.

Grease After 1 Mm.l10 after 60 strokes at 77 F.

The above data indicate that harder greases are prepared where the grease is subjected to a grease-hardening temperature in the range of about 700 to 1100 F. It will be noted also that the temperature of homogenization has no efiect on the worked penetration.

What is claimed is:

1. In a method for preparing a lubricating grease containing a soap-salt complex having a molar ratio of salt to soap in the range of about 7:1 to :1 wherein a greaseforming mixture comprising a lubricating oil, at least one salt-forming low molecular weight carboxylic acid, at least one soap-forming high molecular weight carboxylic acid and a basic reacting compound of at least one grease-forming alkaline earth metal is heated in a grease-making zone maintained at a bulk temperature in the range of about 450 to 600 F. for a period of time suflicient to promote formation of said complex 10 and then cooling to obtain said lubricating grease, the improvement in accordance with which a portion of at least 10% by weight of the contents of said grease-making zone is subjected to a grease-hardening temperature in the range of about 700 to 1100 F. for a period of time sufficient to increase the hardness of said grease.

2. Method according to claim 1 wherein said portion is subjected to said grease-hardening temperature for a period of time sufficient to decrease the ASTM worked penetration thereof after 60 strokes at 77 F. by at least about 10 mun/10.

3. Method according to claim 1 wherein said grease is intimately mixed in said grease-making zone during the grease-making procedure and a peripheral portion of said grease is subjected to said grease-hardening temperature while maintaining the total grease in said grease-making zone at said bulk temperature.

4. Method according to claim 1 wherein said portion which is subjected to said grease-hardening temperature is withdrawn from said grease-making zone and passed through a heating zone wherein said portion is subjected to said grease-hardening temperature.

5. Method according to claim 4 wherein said portion from said heating zone is returned to said grease-making zone.

6. In a method for preparing a lubricating grease containing a soap-salt complex having a molar ratio of salt to'soap in the range of about 8:1 to 25:1 wherein a grease-forming mixture comprising a mineral lubricating oil, at least one low molecular weight carboxylic acid having about 1 to 6 carbon atoms per molecule, at least one high molecular weight carboxylic acid having about 12 to 30 carbon atoms per molecule, and a basic reacting compound of at least one alkaline earth metal is heated in a grease-making zone maintained at an average bulk temperature in the range of about 450 to 600 F. for a period of time sutficient to promote formation of said complex and then cooling to obtain said lubricating grease, the improvement in accordance with which at least about 10% by weight of the contents of said greasemaking zone is subjected to a grease-hardening temperature in the range of about 800 to 1000 F. for a period of time sufficient to decrease the ASTM worked penetration thereof after 60 strokes at 77 F. by at least about 10 mm./ 10.

7. Method according to claim 6 wherein said low molecular weight carboxylic acid is acetic acid, said high molecular weight carboxylic acid is a mixture of hydrogenated fish oil acids and hydrogenated castor oil, and said alkaline earth metal is calcium.

8. Method according to claim 6 wherein the contents of said grease-making zone which are subjected to said grease-hardening temperature are withdrawn from said grease-making zone and are passed through a heating zone wherein they are heated to said grease-hardening temperature by indirect heat exchange with a dense fluid bed of finely divided solids having a temperature in the range of about 700 to 1100 F.

References Cited in the file of this patent UNITED STATES PATENTS 1,912,001 Kaufman May 30, 1933 1,971,750 Lauer Aug. 28, 1934 2,084,974 Kaufman June 22, 1937 2,197,263 Carmichael et al. Apr. 16, 1940 2,222,589 Bradley Nov. 26, 1940 2,487,080 Swenson Nov. 8, 1949 2,564,561 Carmichael et al. Aug. 14, 1951 2,576,032 Morway et al. Nov. 20, 1951 2,735,815 Morway Feb. 21, 1956 

1. IN A METHOD FOR PREPARING A LUBRICATING GREASE CONTAINING A SOAP-SALT COMPLEX HAVING A MOLAR RATIO OF SALT TO SOAP IN THE RANGE OF ABOUT 7:1 TO 40:1 WHEREIN A GREASEFORMING MIXTURE COMPRISING A LUBRICATING OIL, AT LEAST ONE SALT-FORMING LOW MOLECULAR WEIGHT CARBOXYLIC ACID, AT LEAST ONE SOAP-FORMING HIGH MOLECULAR WEIGHT CARBOXYLIC ACID AND A BASIC REACTING COMPOUND OF AT LEAST ONE GREASE-FORMING ALKALINE EARTH METAL IS HEATED IN A GREASE-MAKING ZONE MAINTAINED AT A BULK TEMPERATURE IN THE RANGE OF ABOUT 450* TO 600*F. FOR A PERIOD OF TIME SUFFICIENT TO PROMOTE FORMATION OF SAID COMPLEX AND THEN COOLING TO OBTAIN SAID LUBRICATING GREASE, THE IMPROVEMENT IN ACCORDANCE WITH WHICH A PORTION OF AT LEAST 10% BY WEIGHT OF THE CONTENTS OF SAID GREASE-MAKING ZONE IS SUBJECTED TO A GREASE-HARDENING TEMPERATURE IN THE RANGE OF ABOUT 700* TO 11*F. FOR A PERIOD OF TIME SUFFICIENT TO INCREASE THE HARDNESS OF SAID GREASE. 